media: rockchip/vpu: Add support for non-standard controls

Rework the way controls are registered by the driver,
so it can support non-standard controls, such as those
used by stateless codecs.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>